Mediatomb

MediaTomb is an open source (GPL) UPnP MediaServer with a nice web user interface, it allows you to stream your digital media through your home network and listen to/watch it on a variety of UPnP compatible devices.
Media Tomb website is http://mediatomb.cc/
MediaTomb implements the UPnP MediaServer V 1.0 specification that can be found on http://www.upnp.org/.